The Queen arriving at the London clinic where Prince Philip is recovering

The Duke is progressing according to plans following his operation on Friday and once out of hospital will spend two months convalescing, said the Palace.

The Queen arrived shortly before 7pm at the London Clinic where her husband is being treated.

In a short statement the Palace said: "His Royal Highness the Duke of Edinburgh is progressing according to plans at this early stage. He is comfortable and in good spirits.

"He will remain in hospital for up to two weeks, and it is expected he will then be taking a period of convalescence of approximately two months."

Edward has described the Duke as doing "well" after his visit.

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His visit lasted 20 minutes and as he left he was asked by the waiting press how his father was and replied: "Well, thank you".

The Duke has already received the good wishes of the Prime Minister on his birthday and gun salutes have been fired across the UK to mark the milestone.

David Cameron took to Twitter to send a birthday message to Philip: "Wishing the Duke of Edinburgh a very happy 92nd birthday as he recovers in hospital today."

The King's Troop Royal Horse Artillery fired a 41-gun royal salute at noon in Green Park and this was followed an hour later by a 62-round salvo by the Honourable Artillery Company at the Tower of London.

Gun salutes were fired around the country from Edinburgh Castle in Scotland to Hillsborough Castle in Co Down, Northern Ireland.

The Duke was admitted to the London Clinic for the pre-arranged operation on Thursday, following a garden party at the Palace that day.

Prince Edward said the Duke was doing 'well'

Analysis of the results of the operation are expected to be completed this week.

Details of the original symptoms behind his admission have not been released, but it is thought the procedure did not involve his heart or bladder, organs the Duke has experienced problems with before.

It is believed that Philip has been visited on a daily basis by royal doctor Professor John Cunningham.

Philip's birthday appeared to be remembered by one royal fan who arrived at the London Clinic holding a bunch of white roses, a basket of fruit and a blue balloon with the slogan "Keep calm birthday boy".

The man, who went into the hospital at midday, carried another balloon printed with the message "Feel better".

Security preparations for the Queen's arrival began an hour before her state Bentley pulled up with extra police officers lining the street.

Around 40 members of the public had gathered opposite the entrance to the London Clinic and as the Queen stepped from her chauffeur-driven limousine they cheered.

The spectacle also attracted residents living in apartments overlooking the hospital, who stood on their balconies or looked out of their windows.